In recent years, there have been actively developed vitreous silica crucibles which are used to pull a silicon single crystal and can, with a simple structure, prevent the upper end of the straight body portion thereof from falling inward. As an example of this type of technology, Patent Document 1 discloses a vitreous silica crucible which is used to pull a silicon single crystal and which has a circular groove on the perimeter of the straight body portion thereof and above the initial melt line. This groove is provided in a position below the upper end of a carbon susceptor.
On the other hand, as shown in FIG. 5, Patent Document 2 discloses that by setting the curvature R1 of the inner wall surface of a curved portion 11 of a crucible to 100 to 240 mm, abrupt changes in the area of the melt surface when the melt surface is lowered are suppressed and that by setting the amount of change of the thickness W of the curved portion 11 of the crucible to 0.1 to 1.2 mm/cm, preferably 0.2 to 0.5 mm/cm, the thermal distribution of the curved portion 11 of the crucible is made uniform. Patent Document 2 then discloses that these methods can suppress polycrystallization of silicon and enhance the yield of the single crystal.